Four identical point masses m each are kept at the vertices A, B, and C of a cube having side length ‘a’ (see figure). Another identical mass is placed at the center point D of the cube. (a) Where will you place a fifth identical mass so that the net gravitational force acting on mass at D becomes zero? (b) Calculate the net gravitational force acting on the mass at D.

Answer

At the diagonally opposite corner of C on the floor of the cube `(4Gm^(2))/(3a^(@))`